The present invention relates to elevator systems, and more particularly to elevator systems that use machines with rotors having permanent magnets.
A typical traction elevator system includes a car and a counterweight disposed in a hoistway, a plurality of ropes that interconnect the car and counterweight, and a machine having a traction sheave engaged with the ropes. The ropes, and thereby the car and counterweight, are driven by rotation of the traction sheave. The machine, and its associated electronic equipment, along with peripheral elevator components, such as a governor, are housed in a machineroom located above the hoistway.
A recent trend in the elevator industry is to eliminate the machineroom and locate the various elevator equipment and components in the hoistway. An example is JP 4-50297, which discloses the use of a machine located between the car travel space and a wall of the hoistway. Another example is U.S. Pat. No. 5,429,211, which discloses the use of a machine located in the same position but having a motor with a disc-type rotor. This configuration makes use of the flatness of such a machine to minimize the space needed for the machine in the hoistway. This machine disclosed also makes use of permanent magnets in the rotor in order to improve the efficiency of the machine. These types of machines, however, are limited to relatively low duties and low speeds.
One possible solution to apply such machines to higher duty load elevator systems or higher speed systems is to increase the diameter of the rotor. This solution is not practical, however, due to the space constraints of the hoistway. Another solution, disclosed in PCT Application PCT/FI98/00056, is to use a machine with two motors and a traction sheave sandwiched between the two motors. This solution, however, also exceeds the space limitations of the hoistway and requires the provision of a separate machineroom above the hoistway to house the machine.
The above art notwithstanding, scientists and engineers under the direction of Applicants"" Assignee are working to develop elevator systems that efficiently utilize the available space and meet the duty load and speed requirements over a broad range of elevator applications.
According to the present invention, an elevator system includes a machine having a rotor including permanent magnets and a flat rope engaged with the machine.
Flat rope, as used herein, is defined to include ropes having an aspect ratio, defined as the ratio of width w relative to thickness t, substantially greater than one. A more detailed description of an example of such ropes is included in commonly owned co-pending U.S. patent application Ser. No. 09/031,108, entitled xe2x80x9cTension Member for an Elevatorxe2x80x9d, filed Feb. 2, 1998, which is incorporated herein by reference.
An advantage of the present invention is the size of the machine required to meet duty load and speed requirements. The combination of the improved efficiency of the machine and the torque reduction provided by the flat rope result in a very compact machine that can be fit within the space constraints of a hoistway without adversely affecting the performance of the elevator system. This permits the machine to be located in positions that were previously inpractical.
Another advantage is a reduction in the energy consumption of the elevator system using the present invention. The flat rope results in an engagement surface, defined by the width dimension, that is optimized to distribute the rope pressure. Therefore, the maximum pressure is minimized within the rope. In addition, by increasing the aspect ratio relative to a round rope, which has an aspect ratio substantially equal to one, the thickness of the rope may be reduced while maintaining a constant cross-sectional area of the rope. Minimizing the thickness of the rope results in a smaller diameter traction sheave, which in turn reduces the torque on the machine decreases the size of the motor and may eliminate the need for gearing. In addition, the smaller diameter of the sheave results in an increased rotational speed of the motor, which further increases the efficiency of the machine.
In a particular embodiment, the permanent magnet machine is combined with a flat rope that includes a plurality of load-carrying members and a sheath that surrounds the load-carrying members and is formed from polyurethane. In one configuration, the load-carrying members are formed from an aramid material that produces a high strength, lightweight rope with enhanced flexibility, as compared to conventional round steel ropes. In another configuration, the load-carrying members are steel cords formed from very thin wires, with the wires having diameter of 0.25 mm or less. The use of a sheath formed from polyurethane permits the outer surface of the rope to be optimized for traction.
An advantage of this particular embodiment is the minimal risk of heat damage to the sheath and the load-carrying members of the rope due to use of a machine having a rotor with permanent magnets. In a conventional induction motor, much of the heat losses are in the rotor. This heat loss is conducted directly to the ropes through the sheave. For ropes formed from materials other than steel, which are more temperature sensitive, exposure to such a heat source may lead to degradation of the rope. By using a machine having a rotor with permanent magnets, however, the principle source of heat loss is through the stator and not through the rotor. Therefore, since there is no direct path between the stator and the ropes, the ropes are not exposed to the primary source of heat and the risk of heat related degradation of the materials of the rope is minimized. In addition, the increased efficiency of the permanent magnet machine reduces the total heat generated and therefore further reduces the heating of the ropes.
The foregoing and other objects, features and advantages of the present invention become more apparent in light of the following detailed description of the exemplary embodiments thereof, as illustrated in the accompanying drawings.